1. Field of the Invention
The present invention relates to proper feeding devices contained in image forming apparatuses such as an electrophotographic copying apparatus or a printer having a duplex image forming function and/or a composite image forming function.
2. Description of the Prior Art
Image forming apparatuses heretofore known include an image forming apparatus having an intermediate tray for of containing paper sheets on which an image has been formed and capable of sending out the paper sheets from the intermediate tray to form a second image on the paper sheets. Such as image forming apparatus contains a paper feeding device for sending out from the intermediate tray the paper sheets contained in the intermediate tray and feeding the same in the direction of an image forming section comprising a photosensitive drum, a developing device and the like. This paper feeding device is provided with, for example, (1) a preliminary feed roller provided in a lower part of the intermediate tray for sending out the paper sheets contained in the intermediate tray, (2) a pressure plate for pressing the paper sheets contained in the intermediate tray against the preliminary feed roller to assist in sending out the paper sheets from the intermediate tray by the preliminary feed roller, (3) a feed roller for conveying the paper sheets sent out from the preliminary feed roller in the direction of the image forming section, (4) a pressure roller for pressing the paper sheets sent out from the preliminary feed roller against the feed roller to assist in conveying the paper sheets by the feed roller.
The above described pressure plate can be detached from the feed roller so as not to prevent the paper sheets from being introduced into the intermediate tray. FIG. 4 is a schematic plan view showing a conventional mechanism for detaching a pressure plate from a feed roller. A pressure plate 102 is rotatably supported on a supporting shaft 101 fixed to a frame of an image forming apparatus. An end 102a of this pressure plate 102 is rotatably connected to one end 103a of a crank shaft 103 by means of a pin. The other end 103b of the crank shaft 103 is attached to a disk 109 rotated integrally with a secondary reduction gear 108. The secondary reduction gear 108 is rotated by a driving system 107 of the image forming apparatus through a primary reduction gear 106. The primary reduction gear 106 is connected to the driving system 107 through a spring clutch 105. This spring clutch 105 is intermittently operated by a lever 110 alternately turned to a position represented by a solid line and a position represented by a dot and dash line in FIG. 4. The lever 110 is connected to a rod 104a of a solenoid 104. The pressure plate 102 is rotated around the supporting shaft 101 to be detached from the feed roller or to be brought near the feed roller by exciting the solenoid 104 to bring the spring clutch 105 into a connected state.
However, in the above described paper feeding device, the driving force for detaching the pressure plate 102 from the feed roller is received from the driving system 107 of the image forming apparatus. Accordingly, it is difficult to construct the above pressure plate 102 and a mechanism for rotating the same as an exchangeable unit. Therefore, the paper feeding device has the disadvantage that maintenance thereof takes a lot of time and labor. In addition, the mechanism for rotating the pressure plate 102 is complicated. Accordingly, the paper feeding device also has the disadvantage that the manufacture thereof takes a lot of time and labor and the manufacturing cost thereof is high.